Silicon carbide has excellent physical values. Therefore, by utilizing its characteristic, it is expected to apply the silicon carbide to a power device having high pressure resistance and low loss.
In the case of applying silicon carbide to a silicon carbide vertical metal-oxide film-semiconductor field effect transistor (Metal Oxide Semiconductor Field Effect Transistor: MOSFET) which is one kind of a silicon carbide semiconductor device, a gate insulating film such as a silicon dioxide layer is formed on the silicon carbide.
In the case of forming the silicon dioxide film on the silicon carbide, a method of thermally oxidizing silicon carbide and a method of depositing the silicon dioxide film on the silicon carbide are used. When any of those methods is used, an interface state is formed at the interface between the silicon carbide and the silicon dioxide film. In some cases, the interface state decreases field effect mobility of MOSFET than mobility in a silicon carbide bulk, and increases resistance value of MOSFET in an on-operation state, thereby increasing loss.
To deactivate such an interface state formed in the interface between silicon carbide and the silicon dioxide film, some methods of forming a silicon dioxide film on silicon carbide and then subjecting the film to high temperature treatment in nitrogen monoxide (NO) gas or dinitrogen monoxide (N2O) gas are known.
For example, a method of high temperature treatment in a nitrogen monoxide gas diluted with an inert gas, a method of decreasing a concentration of an oxygen gas generated, and a method of reducing interface defect between a silicon carbide semiconductor substrate and an insulting film are conventionally known (for example, Patent Document 1).
Further, it is known that an interface state density is decreased by heat-treating in a nitrogen monoxide gas under reduced pressure (for example, Patent Document 2).
Further, it is conventionally known that the interface state density is decreased by controlling a partial pressure of a nitrogen monoxide gas by mixing a nitrogen monoxide gas and an inert gas, the inert gas may be He, Ar or N2, and by controlling a volume of a chamber and a flow rate (for example, Patent Document 3).